The present invention generally relates to delivering and injecting fluid into heart tissue. More specifically, the present invention relates to delivering and injecting fluid into heart tissue utilizing an injection array.
Injection catheters may be used to inject therapeutic or diagnostic agents into a variety of organs, such as the heart. In the case of injecting a therapeutic agent into the heart, 27 or 28 gauge needles are generally used to inject solutions carrying genes, proteins, or drugs directly into the myocardium. A typical volume of an agent delivered to an injection site is about 100 microliters. A limitation to this method of delivering therapeutic agents to the heart is that the injected fluid tends to leak and/or disperse from the site of the injection after the needle is disengaged from the heart. In fact, fluid may continue to leak over several seconds. In the case of dynamic organs such as the heart, there may be more pronounced leakage with each muscle contraction.
Therapeutic and diagnostic agents may be delivered to a portion of the heart as part of a percutaneous myocardial revascularization (PMR) procedure. PMR is a procedure which is aimed at assuring that the heart is properly oxygenated. Assuring that the heart muscle is adequately supplied with oxygen is critical to sustaining the life of a patient. To receive an adequate supply of oxygen, the heart muscle must be well perfused with blood. In a healthy heart, blood perfusion is accomplished with a system of blood vessels and capillaries. However, it is common for the blood vessels to become occluded (blocked) or stenotic (narrowed). A stenosis may be formed by an atheroma which is typically a harder, calcified substance which forms on the walls of a blood vessel.
Historically, individual stenotic lesions have been treated with a number of medical procedures including coronary bypass surgery, angioplasty, and atherectomy. Coronary bypass surgery typically involves utilizing vascular tissue from another part of the patient""s body to construct a shunt around the obstructed vessel. Angioplasty techniques such as percutaneous transluminal angioplasty (PTA) and percutaneous transluminal coronary angioplasty (PTCA) are relatively non-invasive methods of treating a stenotic lesion. These angioplasty techniques typically involve the use of a guide wire and a balloon catheter. In these procedures, a balloon catheter is advanced over a guide wire such that the balloon is positioned proximate a restriction in a diseased vessel. The balloon is then inflated and the restriction in the vessel is opened. A third technique which may be used to treat a stenotic lesion is atherectomy. During an atherectomy procedure, the stenotic lesion is mechanically cut or abraded away from the blood vessel wall.
Coronary by-pass, angioplasty, and atherectomy procedures have all been found effective in treating individual stenotic lesions in relatively large blood vessels. However, the heart muscle is perfused with blood through a network of small vessels and capillaries. In some cases, a large number of stenotic lesions may occur in a large number of locations throughout this network of small blood vessels and capillaries. The torturous path and small diameter of these blood vessels limit access to the stenotic lesions. The sheer number and small size of these stenotic lesions make techniques such as cardiovascular by-pass surgery, angioplasty, and atherectomy impractical.
When techniques which treat individual lesion are not practical, percutaneous myocardial revascularization (PMR) may be used to improve the oxygenation of the myocardial tissue. A PMR procedure generally involves the creation of holes, craters or channels directly into the myocardium of the heart. In a typical PMR procedure, these holes are created using radio frequency energy delivered by a catheter having one or more electrodes near its distal end. After the wound has been created, therapeutic agents are sometimes ejected into the heart chamber from the distal end of a catheter.
Positive clinical results have been demonstrated in human patients receiving PMR treatments. These results are believed to be caused in part by blood flowing within the heart chamber through channels in myocardial tissue formed by PMR. Increased blood flow to the myocardium is also believed to be caused in part by the healing response to wound formation. Specifically, the formation of new blood vessels is believed to occur in response to the newly created wound. This response is sometimes referred to as angiogenesis. After the wound has been created, therapeutic agents which are intended to promote angiogenesis are sometimes injected into the heart chamber. A limitation of this procedure is that the therapeutic agent may be quickly carried away by the flow of blood through the heart.
In addition to promoting increased blood flow, it is also believed that PMR improves a patient""s condition through denervation. Denervation is the elimination of nerves. The creation of wounds during a PMR procedure results in the elimination of nerve endings which were previously sending pain signals to the brain as a result of hibernating tissue.
Currently available injection catheters are not particularly suitable for accurately delivering small volumes of therapeutic agents to heart tissue. Improved devices and methods are desired to address the problems associated with retention of the agent in the heart tissue as discussed above. This is particularly true for agents carrying genes, proteins, or other angiogenic drugs which may be very expensive, even in small doses.
The present invention provides an improved apparatus and method for delivering and injecting fluid into heart tissue, or other organ tissues such as liver tissue, bladder tissue, etc. The present invention addresses the problems associated with retention of the fluid in the tissue by utilizing an injection array, such as a plurality of microneedles or a plurality of injection lumens. The present invention may be used to deliver genes, proteins, or drugs directly into the myocardium for purposes of myocardial revascularization.
In an exemplary embodiment, the present invention provides a fluid delivery system including an injection catheter disposed in an elongate sheath. A fluid source is connected to the proximal end of the injection catheter and is in fluid communication with the lumen of the catheter. A nozzle is disposed adjacent the distal end of the injection catheter. In a first embodiment, the nozzle includes a plurality of microneedles each defining an injection lumen in fluid communication with the lumen of the catheter. In a second embodiment, the nozzle defines a plurality of injection lumens in fluid communication with the lumen of the catheter. The first embodiment may be referred to as the xe2x80x9cmicroneedlexe2x80x9d embodiment and the second embodiment may be referred to as the xe2x80x9cneedle-lessxe2x80x9d embodiment.
The microneedles may each have a diameter in the range of approximately 0.005 to 0.05 inches, and a penetrating length in the range of approximately 0.5 to 5 mm. The injection lumens in the microneedle embodiment may have a diameter in the range of approximately 0.00005 to 0.005 inches. Similarly, the injection lumens in the needle-less embodiment may have a diameter in the range of approximately 0.00005 to 0.005 inches.
In both embodiments, the injection lumens collectively form an injection array terminating in a plurality of injection orifices. Fluid is transferred to the injection lumen array from the fluid source through the lumen in the catheter. The injection lumen array distributes the fluid at the injection site over a greater area than would otherwise be achieved with a single needle injection. Thus, the injection lumen array improves fluid retention in the tissue at the injection site.
Also in both embodiments, the catheter and/or sheath may be equipped with an anchor disposed adjacent the distal end thereof. The anchor may comprise a vacuum orifice in fluid communication with a vacuum source via a lumen in the catheter and/or sheath. The vacuum orifice is adapted to stabilize the distal end of the injection catheter and/or the distal end of the sheath.
The sheath may include a hood portion disposed at its distal end. The distal end of the injection catheter may be retracted within the hood of the sheath to reduce the probability that tissue damage will occur when the catheter is advanced through the vasculature of the patient.
The present invention also provides a method of delivering a fluid to heart tissue comprising the following steps. An injection catheter substantially as described above is inserted into a patient""s body and navigated to the desired target site, for example, heart tissue such as the myocardium. The injection catheter may be navigated intravascularly or transthoracicly to the heart tissue. A sheath substantially as described above may also be advanced until its distal end is proximate the target site. The injection catheter is then advanced until the injection array is proximate the target tissue. Fluid is then urged out from the fluid source, through the lumen of the injection catheter, and into the heart tissue via the injection array. The injection lumen array distributes the fluid at the target site over a greater area thereby increasing retention of fluid in the heart tissue at the injection site.
Less than approximately 100 microliters of fluid may be injected into the heart tissue via the injection array. Approximately 0.1 to 20 microliters of fluid may be injected into the heart tissue via each injection lumen of the array. Due to the distribution of the injection array, a substantial amount if not all of the injected fluid is retained in the heart tissue.